Composite materials are lightweight and high-strength materials that may be used for component fabrication in various industries, such as aerospace, automotive, and sports industries. They generally consist of reinforcing elements embedded in a matrix that binds the reinforcing elements together. Organic matrix composites (OMCs) are a class of composite materials in which the matrix consists of an organic material such as one or more polymer resins. The reinforcing elements in OMCs (as well as other types of composite materials) may include fibers such as carbon fibers, glass fibers, boron fibers, and aramid fibers.
OMCs may exhibit a laminated structure in which layers of fibers (or “laminae”) are stacked to provide a desired part thickness and geometry. The fibers in each layer may be aligned in parallel (or “unidirectional”), they may be randomly oriented, or they may be organized in a two-dimensional woven architecture such as a plane weave. In other cases, the fibers may have a three-dimensional woven architecture wherein the fiber threads may be interlocked by three-dimensional weaving.
While OMC laminates may be associated with high in-plane stiffness (i.e., in the plane of the fiber layers), they may exhibit weak inter-laminar strengths such that they may be susceptible to delamination (i.e., the pulling apart of individual lamina in the laminate) and loss in structural integrity, particularly at the exposed surfaces of the laminate part. The susceptibility of OMC composite laminates toward delamination may be greater at contact interfaces between OMC part surfaces and mating structures with different thermal properties, especially when there is relative motion between the OMC part and the mating structure. More specifically, mismatches in the coefficients of thermal expansion (CTE) between OMC components and their mating structures may cause thermal strain at the contact interfaces, leading to possible delamination and structural wear starting at the exposed surfaces of the OMC part. In this regard, it remains a challenge to provide robust connection interfaces between OMC parts and mating structures having differing thermal properties.
An attempt to protect OMC components from high temperature stress using a thermal oxidative barrier coating has been described in U.S. Patent Application Number 2008/0206575. In addition, U.S. Pat. No. 6,132,175 describes the mitigation of contact damage stress between ceramic airfoils and metallic support structures having different CTEs using a multi-layer compliant sleeve that slideably engages a ceramic root and rests between the ceramic airfoil root and the metallic support structure during operation. However, neither of these systems provides a strategy for protecting OMC parts from structural wear at contact interfaces with mating structures.
Clearly, there is a need for systems that mitigate interfacial strain between OMC components and mating structures with thermal expansion mismatches.